A discussion on the validity of Barack Obama’s birth certificate had veteran broadcaster Geraldo Rivera accusing a former adviser to ex-British Prime Minister Margaret Thatcher of “smoking crack.”

The exchange took place Thursday on Rivera’s radio show on WABC Radio in New York City.

Rivera’s guest was Lord Christopher Monckton, a prominent challenger of manmade global warming, who recently met with Arizona Sheriff Joe Arpaio who announced March 1 probable cause exists that Obama’s birth certificate and Selective Service Cards are forgeries.

“I have since had independent investigations made, and have discovered that there are clear irregularities in the document,” Monckton said.

“You’re all smoking crack together,” Rivera interrupted, pressing him to “name one irregularity.”

“I have consulted a 20-year expert in forgery of documents,” Monckton explained, “and I said I want reassurance that this document on the website is genuine. And the guy, having had a good look at it, said ‘I can’t do that.’ He says there are 17 red flags on this document: everything from the number of layers in the document so you can move the stamps about at will, to the fact that some of the document has been oriented incorrectly, the spacing of the words, the spacing of the letters, the number of different typefaces used by what should have been a single typewriter, there are just so many.”

Monckton also said the issue of Obama’s natural-born citizenship had to be cleared up with certainty, since every law signed by Obama could possibly be considered non-valid.

“Because he has signed as president various bills creating criminal offenses,” he noted, “it is open to the lawyers for any of those accused of such offenses to say in their defense, we want to satisfy ourselves that this law is a valid act.”

Also on Rivera’s program was Adam Peck of the left-leaning activist group Think Progress.

Regarding the irregularities discovered on Obama’s purported birth certificate, Peck said, “I’m sure I could scan in the Declaration of Independence and find some irregularities like via Photoshop. It’s fault science based on technological anomalies.”

Peck also took aim at Maricopa County Sheriff Arpaio.

“This notion that Sheriff Joe Arpaio is one of the United States pre-eminent sheriffs is like saying Chef Boyardee is one of the nation’s pre-eminent cooks. I mean it’s absurd. It’s ridiculous. This investigation, if you want to call it that, was certainly not done in an attempt to prove once and for all that President Obama is in fact a U.S. citizen. It was done entirely to find fault with his birth certificate.”